A massive photographic archive of Canada’s Rocky Mountains extending back to the 1880s has revealed that treelines in the range have advanced up the mountains by as much as 250 metres.
“From the 1880s to the 1950s, the Geological Survey of Canada and the Dominion Land Survey sent teams into the Rockies to develop maps in use today,” writes The Canadian Press. As part of this process, “crews took carefully annotated, high-resolution photographs everywhere they went—120,000 of them, now the largest such archive in the world.”
Since the 1990s, teams working for the University of Victoria’s Mountain Legacy Project have been re-photographing the scenes. “There are now more than 8,000 image pairs,” notes CP.
By studying 104 of these pairs, the researchers discovered “a huge amount of change”—not only in the extent of the treelines’ upward shift, but also in the density of the forest. “Almost all the mountains that we were looking at are changing quite significantly,” said University of Waterloo professor Andrew Trant, one of the researchers working on the project.
A stroke of historical luck meant the old and new images were actually comparable, notes CP. “Because the early photos were taken with the best equipment of the day—from large view cameras with glass-plate negatives to high-quality Hasselblad—they permit detailed comparison with the modern images. Researchers were able to zoom in on single trees.”
While land use changes, especially the aggressive suppression of fire, have likely played a role in the upward creep of the treeline, Trant said climate change is “a really important driver” of a process that is shrinking the alpine—and, along with it, an important habitat for many species.